What is not possible for man is possible with God, for with God all things are possible. The way back to God is the same as the way to God: through Christ's already finished work. Our labor is to enter His continuing sabbath rest. "Only believe".
Falling away is not a light thing, nor should it be. But God is able to give you the victory. Not only that, He will use your experience to deepen you, to help others and to establish the kingdom, because many have fallen away and need help back.
Keep abiding in Him. Hold fast to the completed work done on your behalf. Claim the precious Blood as your own, and do not give in to the enemy even for a moment. Remember Christ's promise to give rest to all who come to Him (Mt 11). Be patient and persistent, humble but confident. Because Jesus paid it all, we go to the throne of
grace, not judgment, for help in time of need.
And after you have suffered a little while, the God of all grace, who has called you to his eternal glory in Christ, will himself restore, confirm, strengthen, and establish you. -1Pet 5:10